Sao Paulo: A coronavirus vaccine developed by China’s Sinovac Biotech was 78 per cent effective in a late-stage Brazilian trial and entirely prevented severe COVID-19 cases, researchers said, although a lack of data details stirred calls for more transparency.

The announced efficacy, closely watched by developing countries counting on the vaccine to begin mass inoculations to help end a raging pandemic, was below preliminary findings from Turkish researchers and lacked detailed data provided on US and European vaccines.

The director of Brazilian biomedical centre Butantan Institute, Sinovac’s research and production partner, said detailed results of the CoronaVac vaccine were being submitted to health regulator Anvisa as part of a request for its emergency use.

“One thing is a presentation at a news conference. It’s something else to get the data and analyse it, which is what Anvisa will do,” said Cristina Bonorino, who sits on the scientific committee of the Brazilian Immunology Society. “If it’s what they say, that’s an excellent result,” she added.

Health workers push a patient suspected of having COVID-19 into the HRAN Hospital in Brasilia, Brazil, on Thursday.Credit:AP

Brazil and Indonesia, which have the most COVID-19 cases in Latin America and South-east Asia, respectively, are preparing to roll out the vaccine this month. Turkey, Chile, Singapore, Ukraine and Thailand have also struck supply deals with Sinovac.

Although CoronaVac’s efficacy falls short of the 95 per cent success rate of vaccines from Moderna or Pfizer/BioNTech, it is easier to transport and can be stored at normal refrigerator temperatures.

Health workers test people for COVID-19 at the Indigenous Park, a tribal community in the outskirts of Manaus, Amazonas state, Brazil, where medical care is scarce.Credit:AP

The 78 per cent efficacy rate would also be well above the 50 per cent to 60 per cent benchmark set by global health authorities for vaccines in development early in the pandemic, given the urgent need.

Moderna and Pfizer/BioNTech released detailed results of late-stage trials last year, before receiving emergency use authorisations in the United States and elsewhere.

Butantan Director Dimas Covas told a news conference that full CoronaVac data would be released in an unspecified scientific publication but did not provide a timeline.

Pressed by journalists, Covas said there had been 218 COVID-19 cases in the trial of 13,000 volunteers. Just over 160 of those cases occurred among participants who received a placebo and the rest were in vaccinated volunteers, he said.

Governor of Sao Paulo Joao Doria holds a box of the trial CoronaVac vaccine by China’s Sinovac last year. Credit:Getty Images

Brazil’s CoronaVac trial included elderly volunteers, unlike other studies of the vaccine.

Covas said CoronaVac had entirely prevented severe COVID-19 cases among the vaccinated group, including the elderly. None of those who received the vaccine became ill enough to require hospitalisation, he added.

But piecemeal disclosure of results from global CoronaVac studies have led to concerns about transparency of the trials.

Relatives attend the burial of 71-year-old Jose Abelardo Bezerra, who died from COVID-19 related complications, in Rio de Janeiro on Thursday.Credit:AP

Dr Gregory Poland, a virologist and vaccine researcher with the Mayo Clinic in Rochester, Minnesota, complained that the news from Brazil was “bereft of any real detail”.

“I want to see the data. I want to understand the methods and what was done. And I want to see an actual peer-reviewed publication, not a press release,” he said.

The partial disclosure by Butantan, which had delayed its announcement three times, citing obligations to Sinovac, added to scepticism about the Chinese vaccine in Brazil. Nearly half of Brazilians said they would not take a COVID-19 vaccine developed by China, according to a December poll.

Brazilian President Jair Bolsonaro has expressed disdain for the Sinovac vaccine, citing doubts about its “origin”. He has traded barbs with political rival João Doria, the governor of Sao Paulo, which is funding trials and production of the vaccine.

Brazil has the world’s second-deadliest outbreak after the United States. Its death toll from the virus passed 200,000 on Friday (AEDT) rising 1524 in the previous 24 hours to a total of 200,498, according to data released by the Health Ministry. The country aims to vaccinate 51 million people, or about one-fourth of its population, in the first half of 2021, although immunisations have not yet begun.

Doria reiterated that Sao Paulo, the country’s most affluent and populous state, expected to start vaccinations on January 25.

Based on traditional vaccine technology using inactivated coronavirus to trigger an immune response, CoronaVac can be stored at temperatures of 2-8 degrees Celsius and may remain stable for up to three years.

Vaccines offered by Pfizer/BioNTech and Moderna use a novel synthetic messenger RNA (mRNA) technology, requiring far colder temperatures for shipping and storage. The Pfizer/BioNTech vaccine must be kept at a sub-Arctic temperature, making it an ineffective option for poor nations and areas without the required cold storage equipment.

Reuters

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